Boiler Unit

ABSTRACT

The invention is concerned with an integrated unit comprising a unitary boiler and gas cleaning apparatus. Preferably the integrated unit comprises a boiler unit, and gas cleaning apparatus, the integrated unit has a reaction unit and further comprises a radiant zone connected to the reaction unit, the radiant zone being connected to a convection zone. The integrated unit further comprises a heat exchange means encircling at least one of the radiant zone and the convection zone, and gas cleaning means is preferably provided around at least a part of the heat exchange means. The reaction unit may comprise a fluid bed boiler, gasifier or pyrolytic chamber and wherein fuel is burned completely; burned under pyrolytic conditions; or is gasified. The heat exchange means may comprise an annular heat exchange chamber and the gas cleaning means may be provided in an annular gas cleaning chamber encircling the heat exchange chamber.

This invention relates to a solid fuel fired boiler unit includinggasifiers and pyrolisers, and methods and apparatus for cooling andcleaning gas from such units. The method and apparatus can be used incombination with a fluid bed boiler or in combination with a grate stylecombustion unit or any other solid fuel fired boiler combustion,gasification or pyrolising system.

Boiler, gasifier and pyrolising units such as fluid beds are well known.In such supply units a fluid bed boiler is provided, the fluid bedboiler having a combustion, gasification or pyrolising chamber and fuelis fed to that chamber. Waste gases or syngas pass from the chamber to aradiant chamber then pass to a convector section or chamber to cool thegases. Gases exiting the chamber are typically transferred to a separatecleaner unit. Sorbent is injected into the gas flow prior to entry tothe cleaner unit. The cleaner unit typically comprises a bag filter anda baffle system arranged to direct flow of the waste gases into the bagfilters. On exit from the cleaning unit gases are transferred by pipesto a chimney.

There is a need for an improved boiler and gas cleaning system.

According to a first aspect of the invention there is provided anintegrated unit comprising a unitary boiler and gas cleaning apparatus.

Preferably the boiler is a fluid bed boiler. In other embodiments theboiler may be a combustion grate boiler, gasifier or pyroliser. Theboiler may comprise a combustion fluid bed boiler. In other embodimentsthe boiler may comprise a pyrolysis boiler or a gasification boiler.Desirably a radiant zone and a convection zone are provided within theintegrated unit in fluid communication with gas cleaning apparatuswithin the integrated unit. The radiant zone may be a radiant chamber.The convection zone may be a convection chamber. Preferably theconvection chamber is contiguous with the radiant chamber.

Traditionally each section of plant: fluid bed boiler comprising aradiation chamber and a convection chamber; sorbent injector; gascleaner comprising a filter chamber, and coolant chimney have beenseparately designed and built. Each section is the responsibility of aseparate supplier and the gases are transferred from one section to thenext by pipework. Such an arrangement lacks cohesiveness and preventsachievement of a compact and efficient design.

The inventor has realised that designing an integrated unit combiningand integrating a boiler unit and gas cleaning apparatus can lead tosignificant improvements in design and to a compact integrated unit thatprovides all the functions previously supplied by a number of separatecomponents. The integrated unit comprising a unitary boiler and gascleaning apparatus provides a single component instead of severalseparate components and transfer of the gases from one section toanother is made efficiently and within a compact footprint. Furtheradvantages and improvements are described below. The integrated unit andimproved design provides an advantageous layout and increases theefficiency of extraction of heat energy and reuse of the heat energy inthe system or to generate heat energy. Further the integrated unit canbe installed on the power generation site as a single unit with acompact footprint, so providing significant advantages over the existingmulti-section systems.

Preferably the boiler comprises a reaction unit comprising a chamber inwhich combustion, gasification or pyrolysis occurs. The reaction unitmay comprise a zone such as a combustion zone.

In a preferred embodiment of the invention there is provided anintegrated unit comprising a boiler unit having a reaction unit, and gascleaning apparatus, the integrated unit comprising a radiant zoneconnected to the reaction zone, the radiant zone being connected to aconvection zone, the integrated unit further comprising a heat exchangemeans encircling at least one of the radiant zone and the convectionzone, and gas cleaning means being provided around at least a part ofthe heat exchange means.

Preferably the reaction unit comprises a combustion zone which may income embodiments comprise a fluid bed burner, which will be described inmore detail below. Typically the fluid bed is arranged to combust orgasify solid fuels such as landfill waste, biomass or coal. The reactionunit is connected to a radiant zone which desirably is in the form of aradiant chamber. Preferably the radiant zone is positioned above thereaction unit. Desirably gases can flow freely from a combustion zone ofthe reaction unit to the radiant zone. Preferably the radiant zonecomprises a radiant chamber acting as a cold black body and absorbingheat from the reaction unit into the boiler fluid. The radiant chamberis preferably arranged to facilitate maintenance of a temperature of thereaction unit at a desired temperature or in a desired temperaturerange.

Desirably the radiant chamber facilitates maintenance of the temperaturein the fluid bed in a desired temperature range by extracting heat intothe boiler fluid. In one embodiment the temperature in the fluid bed isheld between 600° C. and 1200° C. and more preferably between 700° C.and 1100° C. and most preferably between 800° C. and 1000° C.

Preferably the temperature in the radiant chamber is between 800° C. and1000° C. Desirably gases passing from the fluid bed are resident in theradiant chamber for a period of time. The gases may be resident in theradiant chamber for between 0.5 seconds and 5 seconds or between 1 and 4seconds. Preferably the gases are resident in the radiant chamber for atleast 1 to 3 seconds. In a particularly preferred embodiment the gasesare held at a temperature of at least 850° C. for at least 2 secondsfollowing injection of secondary combustion air. A portion of the timeat a temperature of greater than 850° C. may be in the fluid bed and aportion of the time may be in the radiant chamber. Desirably the gasesare held at a temperature of greater than 850 C for a period of timelong enough to combust products such as hydrocarbons, dioxin and furans.Desirably the period of time is sufficient to comply with legalrequirements.

In desirably maintaining the gases at a temperature of greater than 850°C. for at least two seconds overall the system complies with currentlegal requirements on treatment of waste and so may ensure that wasteproducts are fully combusted such that hydrocarbons, dioxins and furansare destroyed.

In a preferred embodiment the radiant zone is fluidly connected to theconvection zone. Desirably the radiant chamber is located above thereaction unit. Preferably the convection zone is fluidly connected tothe radiant zone and is desirably distal from the reaction unit. Theradiant zone and the convection zone may be freely connected.

Preferably there is not a physical barrier between the radiant zone andthe convection zone. In a preferred embodiment the convection zonecomprises a convection chamber. In some embodiments the radiant zone andthe convection zone may be regarded as separate zones of a singlechamber. The skilled person will appreciate that the radiant zone andthe convention zone have separate functions that will be well known toand understood by the person skilled in the art.

In a preferred embodiment the radiant chamber comprises a chambersurrounded by a heat exchange means. The heat exchange means maycomprise a helically wound heat exchange coil.

In a preferred embodiment the convection chamber comprises a chambersurrounded by a heat exchange means. Preferably the heat exchange meanscomprises a helically wound heat exchange coil. The heat exchange coilwhich extends around the convection chamber may be fluidly connected toor continuous with the heat exchange coil surrounding the radiantchamber.

Preferably gases flowing from the fluid bed and into the radiant chamberflow on to the convection chamber and a directing means diverts the flowof the gases to flow through the or each heat exchange means surroundingthe convection chamber and the radiant chamber. Desirably the heatexchange means is provided in an annular heat exchange chamber whichsurrounds the radiant and the convection chambers. In a preferredembodiment a direction of flow of the gases through the heat exchangechamber is substantially downward and substantially parallel to adirection of flow of the gases from the fluid bed to the radiant chamberand the convection chamber.

The gas cleaning means is provided around at least part of the heatexchange means. In a preferred embodiment the gas cleaning means isprovided in an annular gas cleaning chamber surrounding the heatexchange chamber. Desirably gases flowing from the heat exchange chamberare directed to flow around a U-turn and into the gas cleaning chambersuch that the gases preferably flow upwardly through the gas cleaningchamber parallel to gases flowing downwardly through the heat exchangechamber.

In a preferred embodiment sorbents may be injected into the gas flow asthe gases exit from the heat exchanger chamber and are directed into thegas cleaning means in the gas cleaning chamber.

Preferably the gas cleaning means comprises a number of bag filtersarranged in the gas cleaning chamber. Desirably the bag filters arearranged in groups around the annular chamber. A number of bag filtersmay be provided in or along a notional radially extending line which maybe considered to be extending from a centre of the convection chamber.Further bag filters may be arranged along additional radially extendinglines such that a segment of an arc around the gas cleaning chamber maycontain a number of bag filters spaced regularly around an arc of thegas cleaning chamber. In a preferred embodiment the gas cleaning chambercomprises a number of sub-chambers. Each sub-chamber may comprise an arcof the annular chamber. In some embodiments bag filters are provided ineach sub-chamber. In another embodiment one or more sub-chambers may nothave bag filters. Desirably each sub-chamber is provided with a gas flowcontrol means. In a preferred arrangement the gas flow control means isprovided downstream of the bag filters. The gas flow control means maycomprise a baffle or alternatively a valve.

Desirably each bag filter comprises a fabric filter fitted around ametal support and arranged to hang within the annular gas cleaningchamber. Suitable bag cleaning filters are well known in the art. Inother embodiments the bag filter may be formed from a ceramic materialor a metallic materiel for use with higher temperature gases. In someembodiments the bag filter may comprise a metal material. The metalmaterial may be in the form of a metal fibre or thread coiled in arandom manner. The metal support may be arranged downstream of thefilter material in order to prevent the fabric filter from collapsing.The metal support may be formed from stainless steel. Preferably thefabric filters are arranged to remove particulate material from thegases. The particulate material may be ash. The particulate material maycomprise other solid materials. Preferably the filters are arranged toremove any particulate material having a diameter above 0.1 microns.

Desirably as the gas flows towards the bag filters sorbents, typicallyin powder form, are injected into the gas flow and desirably thesorbents react with components within the gases to remove sulphur,chlorine and other pollutants from the gas flow.

Sorbents typically form compounds with the sulphur, chlorine etc. andthese solid components are then collected by the bag filters as thegases pass through the filters. The sorbents may be any suitablesorbent. Typically the sorbent may be one of sodium bicarbonate,activated carbon, or lime. Other suitable sorbents may be used as iswell known to the person skilled in the art. The bag filters preferablyalso remove dust and any other particulate material from the gasses asthey pass through the bag filter. There may be a significant amount ofparticulate material in the gases when the fuel is biomass or landfillwaste. The particulate material may typically be ash.

It will be appreciated that as a sorbent is injected into the gases thesorbent material is drawn towards the bag filters. The sorbent materialmay react with pollutants in the gases prior to reaching the bagfilters. It has been appreciated that the sorbent material can desirablycollect on the filter material of the bag filters and that the gases canbe drawn through the sorbent material and then through the bag filterbefore passing downstream towards a cooling chimney. It has thereforebeen appreciated that an increased flow of gases through the sorbentmaterial may increase the amount of sorbent material that is able toreact with the pollutants in the gases and desirably locks morepollutants into a solid compound that preferably is not able to passthrough the filter material.

This is a particular advantage over existing bag filters in whichsorbent is injected prior to entry of the gases into the filter chamber.In the prior art filter chambers a complex series of deflectors have tobe provided in order to direct the flow of gases to the bag filters. Insuch existing filter chamber units sorbent material that does not reactquickly with the pollutants in the gases tends to fall to a base of thefilter chamber and out of the gas flow and so is no longer readilyavailable for reaction with pollutants in the gases.

It has been appreciated that the arrangement of the heat exchangechamber and the gas cleaning chamber are particularly advantageous. Asdescribed before the heat exchange chamber is preferably arranged as anannular chamber around the radiant and/or convection chamber orchambers. Desirably the gas cleaning means is provided in an annular gascleaning chamber. In a convenient and compact arrangement the gascleaning chamber may surround the heat exchange chamber. The gasesexiting from the heat exchange chamber may be directed by the U turn atthe bottom of the heat exchange chamber such that they may flow upwardlyaround the annular chamber and the direction of flow is desirablyarranged to be directly towards the bag filters.

Further it has been appreciated that in the novel apparatus the sorbentmaterial may be directed toward the flow of gases and towards the bagfilters such that the sorbent material may be held in the direct path ofthe gases, in contrast to existing gas cleaning units in which sorbentmaterial tends to fall to the floor of the filter unit due to thecomplex gas flow path.

It will be appreciated that over time particulate material may build upon the upstream side of the bag filters. This particulate material maybe removed from the bag filters using a pulse of compressed air appliedto a downstream side of the bag filter and which passes through the bagfilter. The compressed air may be arranged to push the bag filter in areverse direction and force the particulate material off the filtermaterial of the bag filter. The particulate material preferably fallsfrom the bag filters to a floor of the gas cleaning chamber anddesirably collects at a base of the gas cleaning chamber. A means forremoving the particulate material may be provided and will be describedin more detail below. The means for removing the particulate materialmay comprise a moving floor as will be further described in more detail.It will be appreciated that the described removal means overcomes aparticular difficulty with removing particulate material from an annularfloor of the chamber. Traditional gas cleaning chambers typicallyutilise an Archimedes screw arrangement to remove waste particulatematerial from a hopper and it will be appreciated that such anarrangement cannot be used in an annular chamber.

A downstream side of each of the bag filters is preferably connected toan air pressure source which can be arranged to supply pulse air jets toone or more of the bag filters. A suitable solenoid valve and air supplyis preferably provided downstream from the bag filters. The solenoidvalve and air supply is desirably controlled by control means which maybe connected to a central control means. The bag filters may be cleanedin response to a cleaning schedule or in response to signals from a flowmeter.

Desirably bag filters are arranged in groups within the or each subchamber forming an arc of the gas cleaning chamber. Optionally the valveor baffle or other flow control means may be provided downstream of theor each sub-chamber. In a preferred embodiment pulse air may be providedto a group of bag filters within each sub-chamber of the gas cleaningchamber. Typically pulse air may be supplied to a group of 1 to 50 bagfilters, or from 2 to 40 bag filters, or from 5 to 20 or most preferablyfrom 8 to 16 bag filters. The group of bag filters to which air issupplied may be arranged in a radial line or may comprise a number ofradial lines such that a portion of an arc is cleaned at a time. Thepulsed air may be supplied to all bag filters in a sub-chamber.

Advantageously pulsed air is applied to one sub-chamber at a time.Optionally, the flow control means may be closed before pulse air issupplied to the bag filters. Desirably once the flow control means isclosed cooled exhaust air flows through the remaining sub-chambers ingas cleaning chambers. Desirably the flow of gas is diverted away fromthe closed sub-chamber. In a preferred embodiment the pulsed air appliedto the bag filters dislodges the particulate material which readilyfalls to the moving floor. An advantage of the arrangement is that oncethe flow control means is closed the flow is diverted away from theclosed sub chamber and the air upstream of the bag filter is stagnant.Accordingly the pulsed air flows readily through the bag filters sincethere is little or no gas flow counter to the pulsed air. Particulatematerial is readily dislodged from the bag filters.

Gases which pass through the bag filters in normal operation may bedeflected and directed to a central outlet point. An induced draught fanis preferably provided in the outlet. The induced draught fan ispreferably arranged to draw gases through the bag filters. Desirably theinduced draught fan also controls flow of the gases through the outletand into a chimney.

Preferably the chimney is mounted directly above the integrated unit. Inone preferred embodiment the chimney extends centrally above the outlet.It will be appreciated that the overall footprint of the boiler, cleanerand chimney is greatly reduced compared to the existing designs.Furthermore, the flow of gases is controlled within the unit and it isnot necessary to transport the gases from one section to another.Extraction of heat energy from the system will be further described inmore detail below.

Desirably the exhaust gas is arranged to flow through a measuringdevice.

In an alternative preferred embodiment the outlet directs the exhaustgas flows through a duct and to a measuring device. The measuring devicemay be used to measure species in the exhaust gases. Regulationsrelating to pollution control specify limits to pollution species suchas chlorides, hydrochlorides, sulphides, sulphur dioxides; nitrogenoxides and particulate material. Other species may also be monitored.

Testing methods specify that gases should flow a certain distance alonga linear path before entering the measuring device. Exhaust gases mayenter a chimney or vent that is laterally located or exhaust gases maybe returned to a central chimney.

As referred to above particulate material from the upstream side of thebag can be removed from the filter and deposited on the floor of the gascleaning chamber. Over a period of time particulate material may collecton the floor of the gas cleaning chamber and it would be desirable toremove the particulate material from the gas cleaning chamber.Preferably at least a portion of the floor is arranged to be rotatable.In some embodiments at least a portion of the floor may be arranged tobe openable. In a preferred embodiment a rotatable floor is providedwhich transports particular material to the openable section of thefloor. Particulate material can preferably be removed from the floor ofthe gas cleaning chamber by passing through the openable section of thefloor and into a waste hopper. Desirably when the waste hopper is fullthe waste material can be transported away from the gas cleaningchamber. Typically the waste material may go to landfill.

The rotatable floor of the gas cleaning chamber may comprise a radialconveyor. In one embodiment the radial conveyor may comprise an innersteel plate and an outer steel plate with spacing plates arrangedtherebetween. A device may be provided to rotate one or more spacingplates at a specified location so allowing particulate material to fallinto a waste hopper. A suitable device for rotating the spacing plateback into position is preferably also provided. In a preferredembodiment a single discharge point is provided but it will beappreciated that multiple discharge point could also be utilised. Insome embodiments the openable section of the floor is arranged to beheld in an open position. The inner and outer steel plates may bearranged to rotate. Paddles may be provided arranged between the innerand outer steel plates. Desirably the paddles are adapted to moveparticulate material around the rotatable floor and towards opening.

The arrangement of the fluid bed will now be described in more detail sothat the invention may be better understood. It will be appreciated thatthe fluid bed and reaction unit are conventional and will be wellunderstood by the person skilled in the art.

The reaction unit preferably comprises a fluid bed. The bed maytypically be formed of sand or malachite and high pressure air may besupplied through sparge tube tubes or nozzles in order to fluidise thebed. Recycled flue gas may be used to support fluidisation of the bed.Recycled flue gas may provide a limited supply of oxygen for combustionbut may be advantageous in controlling the temperature of the fluid bedby controlling a rate of combustion occurring in the fluid bed bycontrolling the an amount of oxygen present in the fluid bed.

Desirably the fluid bed reactor uses a solid fuel. Solid fuel may enterthe combustion zone of the reaction unit through a feed chute. The fuelmay typically be a biomass fuel, waste material or may be coal. Othersolid fuels may be used as well or instead of biomass fuels and wastematerial.

Combustion is typically in two stages and secondary air may be suppliedthrough a secondary air manifold at an intermediate part of the reactionunit. The secondary air supply may be controlled to provide a desirablemixture of gases and in particular a desirable mix of oxygen within thegas in order to provide complete combustion.

In the case of a gasifier or pyrolyser secondary air may not beintroduce and the syngas is transferred to the cleaning unit forcombustion thereafter in an engine or gas turbine.

A start-up burner is preferably also provided to initiate combustion.Typically, on initiation of the start-up burner, the bed will achieve atemperature of around 600° C. Once fuel is fed into the bed a workingtemperature of 800° C. may be achieved. It will be appreciated thatother temperature ranges may be used for specific fuels or generated byspecific fuels.

In the case of a combustion unit, as previously mentioned, it isdesirable that the fuel has a residence time of at least 2 seconds atapproximately 800-850° C. after introduction of the secondary air forcomplete combustion. This residence time is specified under currentstandards in order to ensure that pollutants are fully combusted andremoved from the waste gases. Typically pollutants might comprisehydrocarbons, dioxins and furans. It will be appreciated that theresidence time may be partially within the reaction unit and partiallywithin the radiant zone as discussed above.

It will be appreciated that the solid fuels may typically comprise asolid material and that the fuel may be contaminated with othercomponents such as stones, or tramp metal. Contaminants may comprise amaterial that typically does not burn. The reaction unit is desirablyarranged such that contaminants will fall into the fluidised bed andthat they will gradually drop to the bottom of the fluidised bed. Itwill be appreciated that over time a build-up of such contaminants inthe fluidised bed will prevent fluidising of the bed. Desirablytherefore the boiler is arranged to allow ash drawdown periodicallywhich will remove the contaminant material with the ash. In somearrangements an ash drawdown may be carried out on each shift or once aday. In some embodiments fuel may be fed to the reaction unit at a rateof approximately from 1 to 20 tonnes of fuel per hour.

It will be appreciated that typically approximately 40% combustion offuel may occur in the fluidised bed at a temperature of approximately800° C. Typically 60% of the combustion may occur with the secondary airsupply, usually above the fluidised bed. In the absence of a radiantchamber the temperature of the secondary combustion zone can reach 1200C to 1300° C. However, as described above it is desirable that thetemperature in the combustion zone is maintained at approximately 900°C. and as described above the radiant zone can act as a cold black bodydrawing heat from the upper part of the combustion zone.

In other embodiments the boiler may be configured to operate withoutcomplete combustion and to operate under pyrolytic conditions.

Alternatively the boiler may be configured to operate in conditions ofincomplete combustion such that the boiler operates as a gasifier. Thegasifier may be arranged to produce synthetic gas. The synthetic gas maybe used as a fuel gas for a gas turbine.

The arrangement of the heat exchanger means will now be described inmore detail.

In a preferred embodiment the radiant and the convection chambers arelocated above the fluidised bed burner. In a particularly preferredembodiment the radiant and the convection chambers extend axially fromthe fluidised bed burner. In one embodiment the radiant and theconvection chambers are defined by helically wound heat exchange tubes.Desirably the heat exchange tubes are water filled. Preferably waterflowing in the heat exchange tubes is preheated to a temperature rangingfrom 100° C. to 530° C. or more preferably from 150° C. to 300° C. ormost preferably from 180° C. to 270° C. Desirably water flowing in theheat exchange tubes is also pressurised to a pressure of from 1 to 150bargauge or more preferably from 1 to 90 bargauge or most preferablyfrom 5 to 70 bargauge.

Desirably an upper portion of the radiant chamber merges with theconvection chamber. In a preferred embodiment an upper part of theconvection chamber extends to a ducting extending over the axiallyextending radiant and convection chambers and the ducting preferablydirects gases from the convection chamber towards the heat exchangechamber.

In a preferred embodiment the heat exchange chamber is provided as anannular chamber extending around the axially extending radiant andconvection chambers. An inner side of the heat exchange chamber isdefined by the heat exchange tubes which extend around the radiant andconvection chambers and an outer side of the annular heat exchangechamber is preferably defined by a second helically wound heat exchangetube.

Desirably the heat exchange chamber further includes an evaporatorcomprising a series of heat exchange tubes extending circumferentiallyaround and within the heat exchange chamber. In a particularly preferredembodiment the heat exchange chamber further comprises an economisercomprising a further set of heat exchange tubes which extendcircumferentially around and within the annular chamber.

Operation of the boiler and heat exchanger is conventional and will notbe further described. It will be appreciated that the heat exchanger iscontrolled to ensure that the heat exchanger coils are maintained at atemperature that is higher than the dew point. The skilled person willappreciate that the presence of sulphur contaminants in the exhaustgases risks production of sulphuric acid in the event that the exhaustgases move below their dew point.

Water from the heat exchanger may be used to provide hot water toheating systems. In some cases the hot water may be used domestic orindustrial or commercial premises. Alternatively the heat exchanger maybe arranged to produce process steam. Process steam may be used as anenergy source in other industrial processes. In other cases superheatedsteam may be generated which may be used to generate power.

In a preferred embodiment the heat exchange chamber extends annuallyaround the convection chambers and the radiant heat chamber and gasestravel axially upwards through the radiant chamber and then traveldownwardly through the convective heat exchange chamber. Desirably asgases reach the bottom of the heat exchange chamber they are deflectedby a flow reverser formed by a base section or U section and thedirection of travel is reversed so that the gases flow upwardlyuniformly from the base section and flow directly towards the bagfilters. Desirably sorbent is injected into the gas flow in a zone closeto the flow reverser.

According to a second aspect of the invention a method of cleaning gasfrom a boiler comprises the steps of passing heated gases from theboiler to a convection chamber and a radiation chamber provided abovethe boiler; providing a heat exchange chamber arranged around andencircling at least one of the radiation chamber and convection chamberand gas cleaning means being provided around at least a part of the heatexchange means.

According to a third aspect of the invention there is provided anintegrated gas cleaning apparatus comprising a boiler, a reaction unit,a radiation chamber, and a heat exchange chamber arranged around andencircling at least one of the radiation chamber and convection chamberand gas cleaning means being provided around at least a part of the heatexchange means and wherein the gas cleaning apparatus further comprisesa moving floor.

In a preferred embodiment the moving floor is rotatable. Desirably atleast a portion of the floor is openable.

In some embodiments the moving floor may comprise a radial conveyor.Optionally the rotating floor comprises an inner steel plate and anouter steel plate. Spacing plates may be arranged therebetween.Desirably one or more spacing plates are provided between the innerplate and the outer plate. In a preferred embodiment at least onespacing plate is arranged to be openable, preferably by rotating. Insome embodiments one openable section is provided. In other embodimentsa plurality of openable sections are provided.

In a preferred embodiment the moving floor comprises a rotating floorhaving at least one paddle extending between an inner band and an outerband and wherein the or each paddle is arranged to move wasteparticulate towards an open section.

The invention will now be described by way of example only withreference to the accompanying figures in which:

FIG. 1 is a perspective view of an integrated boiler and gas cleaningunit in accordance with the inventions;

FIG. 2 is a plan view of the unit of FIG. 1;

FIG. 3 is a sectional view along the line A-A of FIG. 2;

FIG. 4 is a schematic view of a bag filter; and

FIG. 5 is an enlarged view of the area in circle B in FIG. 2

FIG. 6 is a schematic view of an alternative arrangement;

FIG. 7 is a plan view of the embodiment of FIG. 6;

FIG. 8 is a section across the upper portion of the gas cleaningchamber; and

FIG. 9 is a cross-section of a portion of the integrated unit along theline A-A of FIG. 6;

FIG. 1 is a perspective view of an integrated unit 1 comprising a boilerunit 2 and gas cleaning apparatus in accordance with the presentinvention. The boiler unit 2 comprises a fluid bed boiler 4 providing areaction unit having a combustion zone 6. A cylindrical assemblage 8 isprovided above the fluid bed boiler and contains therein a radiant zone10 and a convection zone 12 encircled by a heat exchange means 14. A gascleaning means 16 is provided around the heat exchange means 14 and thewhole assemblage is contained within a cylindrical shell 18. An upperportion 20 of the shell tapers inwardly to an outlet 22 which in use isconnected to a chimney 24.

A plan view of the integrated unit is shown in FIG. 2. The upper portion20 of the shell can be seen to be divided into segments 26. The outlet28 from the upper portion is located over the radiation and convectionchambers. Gases flowing into the upper portion of the shell flow out ofthe outlet 22 into the chimney 24. A substantially even radialdistribution of gases flows into the chimney. An access door 30 is alsoprovided in the upper section of the shell.

The integrated unit will now be described further in relation to across-section view along the line A-A in FIG. 2.

The integrated unit has a base 32 comprising a fluid bed boiler. Thefluid bed comprises a number of sparge tubes 34 which are provided a bedof sand 36. A primary air fan is connected to the sparge tubes. Thesparge tubes 36 are arranged to be spaced across the fluidised bed andrun substantially parallel to one another. A waste outlet 38 is providedat the bottom of the fluidised bed to allow ash and other waste productsto be removed from the fluidised bed periodically. A waste hopper 40 orother means of removing waste material is provided below the wasteoutlet. Waste is removed from the fluidised bed periodically. Thefrequency of removal is typically once a shift or once a day. Thefrequency may be varied according to the quantity of fuel used and thequality of fuel used.

As is the case in a typical fluidised bed burner a burner 42 is providedfor initiation of combustion. Typically combustion may be initiated atapproximately 600° C. and a working temperature of around 800° C. to 900C may be achieved.

A feed chute 44 is provided which delivers fuel material to thefluidised bed. The fuel material may be waste material such as landfillor may be a biomass. Alternative fuels may be used such as, for example,coal.

The fuel material is delivered to the fluid bed burner from an outlet 46above the fluid bed. Fuel falls from the feed chute towards thefluidised bed. Typically around 40% combustion of fuel occurs in thefluidised bed. Pollutants such as tramp metal or inert material that arenot combusted fall through the fluidised bed and can be removed from thewaste outlet as described above.

Secondary air is delivered to the combustion zone of the reaction unitby means of an air supply connected to a manifold 48. The manifold 48delivers air to a mid-to upper portion 50 of the combustion zone. Theair may comprise a mixture of oxygen and other gases. A composition ofthe air may be controlled so that the supply of oxygen in the air isoptimised such that substantially complete combustion of fuel can occurin the combustion zone. Typically up to 60% of the combustion can occuraround the manifold outlets. With significant combustion of fueloccurring in the upper portion of the combustion zone it has been foundthat the temperature in the upper portion of the combustion zone canreach between 1200° C. and 1300° C. As described below this temperaturemay be controlled in use to be lower than 1200° C. Typically thetemperature in the upper portion of the combustion zone is controlled tobe about 900° C.

Gases from the combustion zone 6 of the reaction unit pass upwardly intothe cylindrical assemblage 8 which is located above the fluid bed boilerand is sealed thereto. The cylindrical assemblage 8 comprises an axiallyextending radiant zone 10 and an aligned and axially extendingconvection zone 12. The radiant zone and the convection zone aremutually aligned and the radiant zone 10 extends continuously into theconvection zone 12. The radiant and convection zones are defined byhelically wound heat exchange coils 52 which define a radiant chamberand a convection chamber. Gases from the combustion zone can pass freelyinto the radiant chamber and thence into the convection chamber.

It will be appreciated that the boiler may be operated under pyrolyticconditions. In other embodiments the boiler can be arranged to producesynthetic gas. In some embodiments the boiler may be arranged to operatein a gasification mode.

The radiant zone 10 acts as a cold black body and draws heat from theupper part of the combustion zone 6. The radiant zone controls thetemperature in the upper portion of the combustion zone 6. The radiantchamber is defined by helically wound heat exchange coils 52 throughwhich water at a cooler temperature than the gases is passed and heatenergy is transferred between gases in the radiant chamber and water inthe heat exchange coils.

Gases from the combustion zone may typically reside in the radiant zone10 for a period of time which is sufficient that the particles are heldat a temperature of greater than 850° C. for at least two seconds.Accordingly, the fuel supplied to the combustion zone of the reactionunit is held at a temperature of greater than 850° C. for at least twoseconds. The fuel is desirably completely combusted and unwantedpollutants such as hydrocarbons, dioxins and furans are preferablycompletely combusted and destroyed. Accordingly, the fuel material iscompletely combusted as required by the waste incineration directive.Gases flow from the radiant chamber into the convection chamber, whichas referred to above, is also defined by helically wound heat exchangetubes 52. Cooler water flowing through the heat exchange tubes extractsfurther heat from the gases flowing through the convection chamber.Typically gases exiting from the convection chamber preferably have atemperature which has been lowered to about 870° C.

An insulating cap 54 is provided across the top of the convectionchamber defining a radially extending passage over an upper portion ofthe helically wound heat exchange tubes. Gases from the convectionchamber are deflected by the insulating cap 54 and pass radiallyoutwardly from the radiant chamber before being deflected into theconvective heat exchange means, which comprises an annular heat exchangechamber 14 arranged around the radiant and convection chambers. In thisembodiment an inner wall 56 of the heat exchange chamber is defined bythe helically wound heat exchange tubes 52 which surround the radiantand convection chambers. An outer wall 58 of the annular heat exchangechamber 14 is defined at least in part by further helically wound heatexchange tubes.

The heat exchange chamber comprises an evaporator section 60 and aneconomiser section 62. The evaporator section 60 contains a number ofcircumferentially extending heat exchange tubes 64 which containpressurised water at a pressure of about 22 bargauge.

The economiser section 62 preferably contains a further set ofcircumferentially extending heat exchange tubes 66. The further set ofcircumferentially extending heat exchange tubes 66 also containspressurised water which may typically be at a pressure of from 5 to 70bargauge.

The hot gases flow around the circumferentially extending heat exchangetubes in the evaporator section 60 and the economiser section 62. Thehot waste gases flow downwardly through the heat exchange chamber 14.The hot waste gases typically enter the evaporator section at around850° C. to 860° C. The waste gases lose heat and energy in the heatexchanger chamber and exit from the economiser section at a temperatureof approximately 150° C. Gases exiting from the heat exchange chamberare deflected by a flow reverser 68 formed in a base section such that adirection of flow of the gases is reversed and the gases flow upwardlyinto a gas cleaning chamber which is provided around the heat exchangemeans. The base section also comprises an injection means (not shown)arranged to inject sorbent materials into the gas flow. The sorbentmaterial typically comprises at least one of sodium bicarbonate,activated carbon, and lime. Other sorbent materials may be utilised bythe skilled person instead of or in addition to the sorbents referred toabove. The sorbent materials are used to remove unwanted pollutants suchas sulphur and chlorine from the gases. The sorbent materials areselected to react with the unwanted pollutants and to remove pollutantsfrom the gas stream by binding sulphur and chlorine into a powder form.

The base section comprises at least one waste removal means. In thisembodiment the waste removal means comprises a rotating floor having aninner band 70 and an outer band 72 which are arranged to be rotatablearound the radiant chamber. The inner and outer bands are arranged torotate around the circumference of the base section. Floor spacingplates 74 are provided between the inner and outer bands. These floorplates can rotate on passing over a waste removal device (not shown). Asthe floor plates rotate any waste material on the floor plate passesthrough the operable section and is deposited into a waste hopperlocated below the waste removal device such as a rotary valve air lock.The waste hopper can be transported from a location below the basesection in order to remove waste material via the rotary valve air lock.

A paddle 73 is provided extending between the inner and outer bands. Thepaddle is arranged to move waste particulate material from below thefilter bags and into the openable section such that the wasteparticulate material is deposition on the waste removal device.

As described above gases exiting from the heat exchange chamber have thedirection of flow reversed and pass upwardly into the gas cleaningchamber which is provided in an annular chamber extending around theheat exchange chamber. Bag filters 76 are provided in the gas cleaningchamber and these are arranged to hang vertically in the annularchamber. The bag filters 76 are arranged to be substantially parallelwith one another and also arranged such that a number of bag filtersextend across from an inner side of the annular chamber to the outerside. A number of bag filters are arranged radially in each segment ofthe annular chamber. The bag filters are arranged in the gas cleaningchamber such that the flow of gases is directly towards and in line withthe bag filters. The gases flow substantially parallel to theorientation of the bag filters.

Each bag filter 76 comprises a fabric material is arranged over a steelcage. Typically each bag filter is about 10 cm in diameter. This is thesteel cage supports the fabric material of the bag filter against theflow of gases. Over time particulate material in the gases is removedfrom the airflow by the bag filters. Such particulate material maycomprise ash as a combustion product from the fuel. The particulatematerial may also comprise sorbent material which has been injected intothe gas flow stream. The sorbent material is carried by the gas flowtowards the bag filters. As the sorbent material is carried in the gasflow in the gas cleaning chamber sorbent material is able to react withpollutants in the gases. Both sorbent material which has reacted withpollutants and the sorbent material which has not reacted withpollutants is retained on an upstream side of the bag filters. Furthergases passing through the bag filters are forced to pass through thesorbent material retained in the upstream side and so further absorptionof pollutants can occur.

It will be appreciated that the bag filter may comprise a ceramic fibre.In other embodiments filter can be formed of a wire mesh. The wire meshcan be fine wires meshed together. In some cases the metal may beplatinum. Platinum can have an additional benefit of acting as catalystfor the removal of organic compounds from the gas. The platinum wire mayassist in the removal of carbon monoxide from the exhaust gases.

Gases passing through the bag filter are clean and do not containpollutants such as sulphur and chlorine, furans or dioxins etc. and havealso been cleaned of any ash or particulate material typically down to1.0 microns. It has been found that the gasses meet the legalrequirements for clean air such as are specified in the IntegratedPollution Prevention Control (IPPC) directive.

Gases exiting from the gas cleaning chamber 16 passed into a radialchamber 78 and are directed radially inwardly. The outlet 22 is placedat the centre of the radial chamber 78 and an induced draught fan 80 isprovided in the outlet to draw gases from the radial chamber and todirect them to the chimney 24. The chimney is not shown but is aconventional chimney.

Bag filter cleaning means (not shown) are provided in the upper portionof the shell. The bag filter cleaning means typically comprises apressurised air supply and the manifold connecting the as supplied toeach bag filter. As required in the course of operation, pressurisedvessels can be pulsed into the bag filters in a reverse direction, sodislodging any particulate material on the upstream side of the bagfilters. Typically the pressurised air supply is at 2 to 5 bargauge andis pulsed in order to dislodge the particulate material from theupstream side of the bag filters. A control means also provided tocontrol the supply of air to the bag filters for cleaning purposes. Thepulse air is supplied to bag filters in a section of an arc. Remainingsections of the gas cleaning chamber operate in a normal fashion.Cleaning of the bag filters may operate sporadically or continuously.The section of the gas cleaning apparatus which is being cleaned isrotated around the annulus. A pressurised air supply manifold isprovided in the upper portion. Solenoid valves control supply of thepressurised air to the bag filters.

The access door 30 is provided in the upper portion of the shell toallow access to the air supply manifolds and valves and to allow the bagfilters to be replaced as required or to be serviced.

In an alternative embodiment illustrated in FIG. 6 the boiler and heatexchange chambers are arranged as before. The gases exit from the gascleaning chamber in a centrally located outlet 100 and are then directedinto a duct 102. The duct 102 is arranged perpendicular to the outletduct 100. The duct 102 delivers the exhaust gases to a testing andmeasuring device located within the duct. The measuring device isarranged to measure species in the exhaust gases. Pollution species thatmay be measured include chlorides, hydrochlorides, sulphides, sulphurdioxides; nitrogen oxides and particulate material. Other species mayalso be monitored. Regulations specify the amount of pollutant that maybe in the gases. According to present requirements the gases arearranged to travel in a straight line in the duct for a specifieddistance before entering the measuring device. It is understood thatflow in a straight line for the specified distance leads to linear flow.

Exhaust gases flow from the measuring device flow to a return duct 105and to a chimney 107. In alternative arrangements the exhaust gases maybe returned to a vent that is laterally located.

FIG. 7 is a plan view of the embodiment of FIG. 6. The upper section 20is arranged above the bag cleaning chamber and the duct 102 extends fromthe exhaust outlet 100 from the gas cleaning chamber.

As is best seen in FIG. 8 in the alternative arrangement the gascleaning chambers 106 is divided into sub-chambers 108. Each sub-chamber108 comprises an section of the annular gas cleaning chamber 106. Eachsub chamber 108 comprises an arc of approximately 60° of the annularchamber 106. A first sub chamber 110 does not contain any bag filters.The remaining five sub-chambers 112 each have a number of rows 114 ofbag filters 116. A baffle 118 is provided at a top end of the fivesub-chambers 112 and the baffle controls 118 flow of gas from thesub-chambers 112 to the first sub chamber 110 towards the outlet 120into the duct 102. When the baffle 120 from a sub chamber 112 is closedgases do not flow through the respective sub-chamber 112 and the gasesin the respective sub-chamber 112 are stagnant.

Pressurised air is supplied to an outer manifold 122. The pressurisedair is fluidly connected to a number of inner manifolds 124 each ofwhich is arranged to be able to supply the pressurised air to the bagfilters 116. Valves are provided in each inner manifold to control aflow of pressurised pulse air to the bag filters 116. A controller isarranged to control the supply of air from the outer manifold to the bagfilters 116.

The baffle 118 controls a flow of air from an upper chamber above thegas cleaning chamber towards the measuring device and the chimney.Closing the baffle stops flow from the upper portion of the sub chamberstowards the first sub chamber and into the outlet and duct to themeasuring device. Exhaust gases tend to follow the course of leastresistance and the flow of exhaust gases moves to flow through the subchambers in respect of which the respective baffle remains open.

In the cleaning process one sub-chamber 112 is closed at a time. Oncethe respective baffle 118 is closed the gases are not drawn through theclosed sub chamber and gas flow on the immediately upstream side of thebag filter becomes stagnant. A particular advantage of the arrangementis that the boiler and gas cleaning apparatus can continue to be usedwhile one of the bag cleaning sub-chambers is closed and the bag filterscleaned. The bag filters in the sub-chambers can be cleaned on asequential arrangement. This contrasts with conventional boilers and gascleaning arrangements in which the boiler and gas cleaning apparatushave to be suspended while cleaning of the bag filters is carried out.

In the cleaning process the pulsed air is controlled to be suppled fromthe outer manifold 122 and into the inner manifolds 114. A controllerlocated remotely, is arranged to apply the pulsed air to the bag filters116. Particulate material collected on the upstream side of the bagfilters is displaced by the pulsed air and falls from the bag filter 116and onto the rotatable floor located at the base of the gas cleaningchamber to be removed.

FIG. 9 is a cross section along the line A-A in FIG. 7. The boilerarrangement and the heat exchange apparatus is the same as in FIG. 3. Inthis embodiment the gases flow from the boiler 130 and into the radiantchamber 132 and then into the heat exchange chamber 134. Gases from theheat exchange chamber 134 flow to the base 136 of the heat exchangechamber and then upwardly into the annular gas cleaning chamber. Gasesflowing through the gas cleaning chamber pass through the bag filters116. Particulate material collects on the upstream side of the bagfilters. When the cleaning process is carried out pulsed air passingthrough the bag filters dislodges the particulate material which fallsto the rotatable moving floor 138.

Downstream of the bag filters 116 the gases flow through the respectivebaffle 118 into the first sub-chamber 110 through the baffle and intothe duct 102. The side ducting 102 carries gases to a testing device 104which is compatible with standard testing requirements. The testingdevice is arranged after a section of straight ducting such that the gasflow is considered to be laminar on entry to the testing device.Downstream of the testing device the gases flow through a return valve105 and is discharged into the chimney 107.

The controller is arranged to clean each of the sub-chamberssequentially. An important aspect is that the bag filters are cleanedwhile the boiler is operating and that it is not necessary to stop orinterrupt the operation of the boiler.

1. (canceled)
 2. An integrated unit comprising a boiler unit, and gascleaning apparatus, the integrated unit having a reaction unit andfurther comprising a radiant zone connected to the reaction unit, theradiant zone being connected to a convection zone, the integrated unitfurther comprising a heat exchange means encircling at least one of theradiant zone and the convection zone, and gas cleaning means beingprovided around at least a part of the heat exchange means.
 3. Anintegrated unit according to claim 1 wherein the reaction unit comprisesa fluid bed boiler, gasifier or pyrolytic chamber and wherein fuel isburned completely; burned under pyrolytic conditions; or is gasified. 4.An integrated unit according to claim 1 wherein the heat exchange meanscomprises an annular heat exchange chamber.
 5. An integrated unitaccording to claim 4 wherein the gas cleaning means is provided in anannular gas cleaning chamber encircling the heat exchange chamber.
 6. Anintegrated unit according to claim 5 wherein the gas cleaning meanscomprises an array of bag filters in the gas cleaning chamber andwherein the bag filter comprises at least one of: fabric; ceramic andmetal material.
 7. An integrated unit according to claim 6 wherein theheat exchange chamber and the gas cleaning chamber are arranged suchthat the flow of the gases is directly towards and in line with the bagfilters and wherein the gas cleaning chamber comprises a number of subchambers and wherein optionally the sub-chambers are fluidly separated.8. An integrated unit according to claim 7 wherein a supply ofpressurised air can be applied to a downstream side of the bag filters.9. An integrated unit according to claim 8 arranged to apply pressurisedair in a pulse and wherein the pulse is applied to each sub-chambersequentially and optionally the boiler remains in operation.
 10. Anintegrated unit according to claim 5 wherein a sorbent can be injectedinto the gas cleaning chamber.
 11. An integrated unit according to claim5 wherein waste material can be removed from a base of the gas cleaningchamber.
 12. An integrated unit according to claim 1 wherein the gascleaning chamber comprises a moving floor.
 13. An integrated unitaccording to claim 12 wherein the moving floor comprises a rotatingfloor having at least one paddle extending between an inner band and anouter band and wherein the or each paddle is arranged to move wasteparticulate towards an open section.
 14. An integrated unit according toclaim 1 wherein the radiant zone is positioned above the reaction unit.15. An integrated unit according to claim 12 wherein the convection zoneis in free fluid communication with the radiant zone.
 16. An integratedunit according to claim 5 wherein at least one wall of the annularchamber is formed by at least one helically wound heat exchange tube.17. An integrated unit according to claim 16 wherein the at least onewall also defines at least a portion of the radiant zone and theconvection zone.
 18. An integrated unit according to claim 4 wherein theheat exchange chamber comprises an economiser and an evaporator.
 19. Anintegrated unit according to claim 1 wherein a chimney is centrallylocated above the radiant and convection zones.
 20. An integrated unitaccording to claim 1 having a footprint comprising that of a fluid bedboiler.
 21. An integrated unit comprising a boiler unit, and gascleaning apparatus, the integrated unit comprising a radiant zoneconnected to the boiler, the radiant zone being connected to a reactionunit, the integrated unit further comprising a heat exchange meansencircling at least one of the radiant zone and the convection zone, andgas cleaning means being provided around at least a part of the heatexchange means and wherein the heat exchange chamber and the gascleaning chamber are arranged such that the flow of the gases isdirectly towards and in line with gas cleaning means and wherein the gascleaning chamber comprises a number of sub chambers.